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AIX RamSan 2

Posted on 2014-01-29
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this is 2nd part of the below Q

http://www.experts-exchange.com/OS/Unix/Q_28349015.html

IBM is talking about "ACA"
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Is that an sdd or aix setting (ACA)?

ramsan had it enabled by default.

what is your input here?
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Question by:it-rex
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woolmilkporc earned 500 total points
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Do you mean "Auto Contingent Allegiance"?

That's a form of exception condition handling, exception recovery  and related message passing in the scsi protocol.

ACA is set when a "Check Condition" status occurs
ACA remains in effect until the initiator sends "Clear ACA"
During ACA only certain commands are allowed, marked by the ACA queue tag.

ACA (and CA, ECA which work a bit differently) are firmware driven.

AIX needs ACA being set to enable concurrent command processing. This is because ACA in a way disconnects the exception handling from command processing (a concurrent command can execute if allowed by the ACA queue tag before the recovery procedure for another command has completed).

Afaik on the Flash you can configure ACA on a per LUN basis, which specifies whether to handle check conditions on that LUN following the ACA method.
Again: For AIX, ACA is mandatory. It's not "settable", neither in AIX nor SDD.

On the DS8K, ACA is set by choosing the appropriate "hosttype" for the specific volgrp.

AIX had a problem with MPIO round robin and ACA, because it could happen that multiple "clear ACA" commands were sent, which could affect performance.
AIX 7.1 TL2 SP1 should have this problem fixed, though.


wmp
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by:it-rex
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thanks
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